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Simple integration problem help

  1. Mar 6, 2006 #1
    Could anyone explain to me ultra simply by means of a mechanical approach maybe why the integration of 1/(3-0.2x)dx = -5 ln l 3-0.2x l ? thanks
     
  2. jcsd
  3. Mar 6, 2006 #2

    quasar987

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    set y = 3-0.2x
     
  4. Mar 6, 2006 #3

    What I don't get is the -5 before the ln l 3-0.2x l ?? :-(
     
  5. Mar 6, 2006 #4

    quasar987

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    After you've set y = 3-0.2x, you also have to find dy in terms of dx. Do the calculations and you'll see where the -5 pops in.
     
  6. Mar 6, 2006 #5
    dy = -0.2 and then ?
     
  7. Mar 6, 2006 #6
    right so
    [tex] -\frac{1}{0.2} dy =dx\Rightarrow -\frac{1}{2/10} dy = dx \Rightarrow - \frac{10}{2} dy =dx \Rightarrow -5dy=dx [/tex]

    now substitute back into equation and integrate
     
  8. Mar 6, 2006 #7
    :smile: thanks
     
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